The invention relates to a seat suspension system which isolates a vehicle seat from vibrations.
Passive suspension systems, such as for a vehicle seat, are known. For example, John Deere production 6000, 7000, 8000 and 9000 Series tractors have passive seat suspension systems which include a hydraulic shock absorber in parallel with an air bag.
Active suspension systems are known which include an electro-hydraulically controlled actuator working in parallel with a resilient device, such as a spring. For example, U.S. Pat. No. 4,363,377 (Van Gerpen), issued Dec. 14, 1982, discloses an active seat suspension system with a hydraulic actuator in parallel with a spring. A control system controls fluid communication to the actuator in response to a seat position signal, a stiffness control, a seat height control and a gain control. U.S. Pat. No. 6,000,703 (Schubert et al.), issued Dec. 14, 1999, discloses an active cab or seat suspension control system with a hydraulic actuator in parallel with a pneumatic air spring or air bag. U.S. Pat. No. 6,371,459, issued to Applicant's assignee, describes an active seat suspension system wherein an accelerometer is attached to the seat. However, with an accelerometer attached to the seat, the system cannot respond until an acceleration of the seat occurs and is sensed. Also, such an accelerometer must be connected to wires or cables which are constantly being flexed and which require special care in routing.
A system for controlling the pitch of a truck cab is described in U.S. Pat. No. 5,044,455 (Tecco et al.), issued 3 Sep. 1991. However, this system requires at least front and back acceleration sensors in order to generate cab or frame pitch acceleration signals. Furthermore, such a system cannot control simple vertical acceleration of the cab relative to the frame, it can only control pitch or pivotal acceleration.